This invention relates generally to an improved processing system in which a measured amount of extrudate is severed by a rotating cutting means and deposited in a receptacle traveling on a conveyor, and more particularly, to an apparatus for accurately depositing predetermined quantities of molten polymer extrudate into deeply recessed receptacles (such as caps and crowns which have relatively high sidewalls) to form a lining therein.
Heretofore, extrudate material has been deposited in each crown shell by controlling the rate of extrusion of the extrudate material and then directing this material through one or more rotating cutting blades timed to the feed rate of the crowns past the depositing station. In conventional high speed crown making systems, the speed of the conveyor, the feed rate of the extrudate material, and the angular velocity of the cutting blades are all proportional at any given rate of production. Therefore, for any rate of production, the feed rate of the crowns must be compatible with the cutting rate of the blades, and these in turn must be compatible with the minimum cooling rate of the formed liner.
An illustrative prior art apparatus for forming liners in crowns is described in U.S. Pat. No. 3,360,827 to Aichele, wherein a rotatably mounted blade is rotated in synchronism with the movement of a conveyor. The cutting blade is rotated at a uniform speed that is directly proportional to the speed of shell conveyance. During each rotation of the knife, a segment or pellet of extruded thermoplastic polymer is severed, and the radial tip of a blade enters and exits the recess of a shell as it is conveyed, thereby depositing the polymer pellet centrally therein. A subsequent operation forms the pellet into a desired liner shape.
Although the high feed rate apparatus disclosed in this patent operates satisfactorily for providing thermoplastic material in bottle caps or crowns of the usual shallow type (crown heights of approximately 0.23 inch to approximately 0.267 inch), it is not suitable for the lining of deeply recessed caps such as the twist off type, which have crown heights of approximately 0.6 inch to approximately 0.869 inch. The reason conventional systems such as that described above can not process deeply recessed caps at high feed rates is that the radial tip of the cutting blade can not enter and exit the receptacle recess quickly enough to avoid contact with the receptacle sidewall.
One solution to this problem is disclosed in U.S. Pat. No. 3,782,329 to Everett. The Everett device provides a cam and follower arrangement to elevate the blade during its rotation, thus preventing interference with the cap sidewalls before and after depositing the lining material. The Everett arrangement, however, is subject to rapid wear of its moving parts, is difficult to adapt to high feed rate operation, and is not suitable for commercial mass production. Further, it can not be easily retrofitted into existing crown processing devices.
Another prior art approach to dispensing liner material into deeply recessed receptacles is described in U.S. Pat. No. 4,060,953 to Ohmi. Ohmi discloses that the speed of blade rotation can be varied in a predetermined manner so as to prevent the tip of the cutting blade from contacting the cap shell sidewall. In the Ohmi apparatus, the blade is rotated at a non-uniform speed, in response to the speed of conveyance of the cap shells, such that the speed of the blade gradually decreases as the exterior end of the blade approaches the shell conveying passage and such that the speed of the blade gradually increases as the exterior blade end moves away from the shell conveying passage. The variation in cutting blade rotational speed is achieved by the use of a gear drive system that comprises non-circular gears (e.g., elliptical gears). A disadvantage of the Ohmi system, however, is that for every crown shell design, the user must select, either by trial and error or by a complicated mathematical derivation, a set of non-circular gears which will provide the necessary clearances from the crown shell sidewalls.
A further disadvantage of known high feed rate crown processing devices is that they are not easily adapted for use in cutting and dispensing recently developed thermoplastic polymer extrudates. The newer compounds have longer molding times and therefore require slower feed rates. Hence, in order to utilize them in a conventional high feed rate crown processing system, the conveying speed and the angular velocity of the blade synchronized therewith must be reduced. At lower feed rates, however, the metered quantities of extrudate material are frequently not centered on the crown after being severed by the cutting blade. That the metered quantities of extrudate material are centered on the crowns at high production rates but are not centered at low production rates indicates that the extrudate material absorbs the shock of the cutting blade and elongates rather than being sheared at the proportionally reduced cutting velocity. Further, because transfer of the cut segment from the knife blade onto the receptacle base depends upon adhesion of the segment to the base, decreases in blade speed interfere with efficient transfer by significantly reducing the force with which the segment is deposited within the base.
Seeking to address this failing in the prior art, U.S. Pat. No. 3,955,605 to Zupan discloses a high feed rate crown processing machine which is also capable of accurately severing and depositing extrudate materials at substantially reduced feed rates. The Zupan system includes a variable speed conveyor and a pair of counter rotating cutting blades. The conveyor and cutting blades are driven at speeds independent of each other, and the blades are intermittent in operation so that the blades can be rotated at a sufficient velocity to sever the extrudate without regard to the feed rate. A disadvantage of the Zupan system is that it relies solely on gravity for placement of the severed segment into the crown. Additionally, severed segments tend to adhere to one of the blades. Accordingly, the Zupan system is not suitable for higher production rates, such as above 2000 crowns per minute, which are typically achieved by modern crown processing machines.